(i) Field of the Invention
This invention relates to a method for the recycling and reuse of materials heretofore considered non-recyclable. In particular, it relates to the recycling of a mixture of automobile shredder residue with virgin and/or unsorted post consumer synthetic plastic material.
(ii) Description of the Prior Art
Automobile shredder residue consists predominately of non-metallic solid material including plastic, broken glass, rubber, foam rubber, soil, and fabric. It is an unconsolidated, non-homogeneous solid with a medium to dark brown colour. Individual objects are generally identifiable in the waste material. Pieces of automobile headlights, seat covers, seat cushion foam, broken safety glass, wire, automobile arm rests, and rubber gaskets are typical.
The gross bulk density and compactibility of automobile shredder residue varies with the type of infeed material being shredded, the moisture content, the time allowed for compaction on-site, the non-ferrous component, and other factors related to the specific air or water handling processes at any given facility. The Recycling Research Foundation report "Shredder Residue: Environmental Information & Characterization Under RCRA", March 1992, (the contents of which are incorporated herein by reference), reported a bulk density of 267 kg/m.sup.3. This figure was the mean value of bulk density determinations generated from various studies.
A typical analysis of the composition of shredder residue by component weight is as follows: fabric and carpet: about 45.6%; plastic: about 5.5%; rubber: about 5.1%; wire and metal: about 8.2%; paper: about 2.7%; dirt and miscellaneous: about 22.1%; glass: about 0.3%; foam rubber: about 8.9%; and wood: about 1.6%.
The scrap metal industry is seeking ways to recycle auto shredder residue. Presently, there are no widespread industry solutions. Nevertheless, automobile shredder residue is being mandated for use as landfill cover.
Synthetic plastic materials in one form or another enter into almost every aspect of our daily lives. Expanded polystyrene which is well known and used for its insulation and shock absorbent properties, and is encountered in fast food restaurants as clam shell containers for hamburgers and drink cups, as plates and trays in sandwich bars and fish and chip shops, as pizza trays, as agricultural containers for seeds and plants; as alternative disposable cups and plates etc., to conventional crockery, as cups at vending machines as yoghurt and frozen yogurt pots, as boxes to transport certain perishable foods, e.g., fish and eggs, as fruit trays, and as protective packaging for a wide range of goods, e.g., telephones, so-called white goods, e.g., refrigerators and cookers, and televisions.
Other synthetic plastic materials which are in common use are as follows: polyethylene which as high density and low density polyethylene is used for containers, e.g., refuse sacks, carrier bags and even especially containers, e.g., blood and plastic containers and as expanded polyethylene is used in film or in sheet form for protective wrapping and packaging easily damaged items in the electronics, glass, china and furnishing industries, polystyrene, high impact polystyrene which is used for making cutlery and some kinds of beverage cups; oriented polystyrene as used in the packaging catering and confectionary industry polyvinyl chloride which is somewhat clear and is used for packaging and wrapping films and for containers, e.g., blister type packages for articles of various kinds; acrylonitrile/butadiene/styrene which is used for many kinds of containers, e.g., cups, yoghurt pots and butter and margarine containers; polypropylene which can be very clear and is used in general packaging where a clear view of the packaged article is required without discoloration, e.g., for food containers as the container covers and for packaging clothing, e.g., shirts, and other articles, e.g., sheets and curtains, and expanded polypropylene which is used for its insulation and impact resistance properties as say end blocks for transporting computers and for automobile bumpers or fenders.
Synthetic plastic material usage has increased yearly, and new synthetic plastic materials which are introduced into the market have different physical and chemical characteristics, e.g, melt temperature, hardness and solubility. The reuse of this multitude of synthetic plastic materials having widely different physical and chemical properties is most difficult. The separation of synthetic plastic material types is impossible by visual inspection. Some polyethylene, polyacrylonitrile, polystyrene, polyesters and polypropylene plastics look and feel much the same, but may have widely different melt temperatures. High density and low density polyethylene have greatly different properties. Removing labels from containers is also an economically impossible task. Containers are also made of layers of different materials.
Scrap synthetic plastic materials, as collected from refuse sites, hereinafter referred to as "post consumer plastic", manufacturing operation wastes, household wastes, "fluff" from shredded automobiles and the like are commonly complex mixtures of many diverse waste materials-paper, thermoplastic products, cured thermosetting products, metals, fibrous products, etc. It is difficult and commonly uneconomic to proceed through one or more sorting and separating steps before the recycling process.
Particularly difficult materials to handle in complex scrap mixtures are cured thermoset resins. Conventionally, these will not melt for remolding purposes, even after separation and isolation from scrap mixtures. Also, they are commonly associated with fibrous reinforcements, e.g., glass fibres, which are equally difficult to separate and reuse.
It is a desirable feature to recycle such synthetic plastic materials. Skips which contain glass, cardboard, paper, wood, textiles, metals and plastic films and plastic bottles from domestic and industrial sources can be collected and taken to a recycling plant. One such recycling plant sorts the glass, metals, wood, contaminates, synthetic plastic materials, paper textiles, waste and burnables from each other. The synthetic plastic materials and paper are fed to a bale press, the bales are fed to a shredder, and the shredded synthetic plastic materials washed, dewatered, dried and then sorted with hydrocyclones. The sorted synthetic plastic material is fed to an extruder and the molten plastics passed through a die which produces synthetic plastic material threads that are cut into pellets by means of rotating blades. The synthetic plastic material pellets are packaged to be ultimately formed into lower grade synthetic plastic materials, e.g., coat hangers, flower pots, garden hoses, pipes, sheeting and bottles etc. The synthetic plastic material is downgraded, because of its melt history, being a mixture of different kinds of synthetic plastic materials and cannot take colour pigments, so that the products end up a dull grey/brown/green colour.
Another synthetic plastic material recycling process uses waste articles made mainly from thermoplastics, in particular high and low density polyethylene and polypropylene. Other thermoplastics can be recycled but under certain controls and polyvinyl chloride may only be present in small proportions without special additives being used. The sources of new material for this process are manufacturers of synthetic plastic material articles, i.e., film, bags, tableware, syringes, toys, book bindings, trays, various domestic articles, e.g., containers and bottles, milk, suppliers who produce their own synthetic plastic material milk bottles and who have redundant and broken milk crates, beverage companies who use synthetic plastic material bottles and containers, and who have broken beer crates, large volumes of below standard articles, e.g., piping, ducting, synthetic plastic material joints, synthetic plastic material medical goods, head waste from manufacturers of synthetic plastic material articles from starting up the machine and after shutdown, synthetic plastic material packaging to be disposed of by manufacturers, distributors and retailers and contaminated or sub-standard granules from synthetic plastic material processors.
The collected synthetic plastic material is sorted, granulated, mixed/blended and then plasticized in an extruder consisting of a large steel screw in a heated steel barrel, by means of the friction caused by the rotating screw melting the synthetic plastic materials. Extruders are expensive machinery whose parts are expensive to replace, require skilled and specialist operators. It has been the traditional view that extruders can generally only be used to recycle homogenous synthetic plastic material waste. This process can produce basic solid synthetic plastic material elongated product, e.g., posts, poles, stakes, boards and a variety of similar shaped products, but again the synthetic plastic material is of down graded nature and could not be mixed with virgin synthetic plastic materials. Specific use of the product are slatted floors for farm animals, pallets, underground cable covers, fencing posts and street and road furniture.
Accordingly, synthetic plastic materials produced for reuse from plastics waste which has been recycled cannot compete with regard to cost and quality with virgin synthetic plastic materials, unless one is dealing with uncontaminated factory scrap synthetic plastic materials which can be fed back into the processing chain for extrusion. Contaminated synthetic plastic material waste has to be subjected to a number of operations before it is suitable for granulation or pelletization, e.g., crushing, shredding, sorting, washing, dewatering and drying. Moreover, there is some synthetic plastic material waste, e.g., computer, audio and video tapes and floppy discs which, because they incorporate metal oxide, and are contained by cassettes of different plastics materials, cannot be recycled in currently available recycling plants. Moreover, incineration is prohibited because metal oxides when burnt give off noxious gases.
Accordingly, there is a need for a process which will permit the recycling and reuse into useful products, of complex mixtures of waste materials which include in their composition substantial quantities of cured thermoset plastics materials. It would therefore be desirable to provide a method which would simultaneously solve these two recycling problems, i.e., of automobile shredder residue and post consumer synthetic plastic material, i.e., unsorted synthetic plastic material waste.
Attempts have been made in the past to make chipboard-like products using thermoplastics-containing scrap materials as the binder or glue therein. As is well known, chipboard is conventionally made of wood chips and liquid/powder uncured thermoset resins. The resins, which act as the binder or glue, are pressed into chipboard products in continuous or discontinuous processes, and subsequently cured under heat and pressure so that the wood chips become held together by the polymerized and cured resins (melamine, phenolics, polyurethanes, etc.). Attempts to use mixed thermoplastics scrap resins, sometimes contaminated with other substances, e.g., paper, metals, textiles, wood, etc. have focused on extrusion, kneading and injection molding processes. These would seem to allow recycling of thermoplastic waste directly into finished or semi-finished products, without separation of the components of the waste or intensive washing thereof.
A combination of a melt chamber and an extrusion screw is known which is used to produce molten synthetic plastic material from foamed thermoplastics waste of scraps, odds and ends, chips and cut ends produced during the processing of synthetic plastic materials and synthetic resins for producing good quality recycled pellets. The extrusion screw extends horizontally beneath and is fed from an elongate melting chamber which is V-shaped in cross-section and extrudes threads of plastics through a suitable die.
In another apparatus involving an extruder, the extrusion screw is arranged vertically but this apparatus suffers from the same disadvantages as those of an extruder having a horizontal screw.
Attempts have been made, and are disclosed in the patent literature, to attempt to solve each of these individual problems, but not, heretofore, both problems simultaneously.
U.S. Pat. No. 4,187,352 issued to Klobbie for example, discloses a process in which unsorted thermoplastic synthetic resin waste material is formed into an article having the working and processing properties of wood by subjecting the mixture to a mixing operation in a housing including a screw/kneading member so that it is extruded into a finished product.
U.S. Pat. No. 3,956,541 issued to Pringle discloses a process for making flexible structural members, namely cable reels, using scrap wire and cable insulation, namely polyvinyl chloride, polyethylene, and other scrap materials. The scraps are shredded in combination with the wire remnants, and the wire is separated from the shredded insulation. This scrap is then mixed with phenolic resin, zinc stearate and wood filler, and compression molded to form flexible objects.
U.S. Pat. No. 4,279,790 issued to Nakajima describes the preparation of composite material compositions of waste paper, thermoplastic resins and other additives, mixed together as the paper is dried from a slurry condition. The inclusion of synthetic rubber, normally a thermoset, is suggested in this patent. The final products are formed by injection molding.
U.S. Pat. No. 4,396,566 issued to Brinkmann discloses a process for the continuous manufacture of sheeting from thermoplastic synthetic resins, in which the resin is used in the form of particles and passed continuously through a preheating zone, and then through a treatment zone, in which it is pressed and compacted to form a visually appealing flexible sheet material. The possibility of using waste strips of thermoplastic synthetic resin is disclosed.
U.S. Pat. No. 4,427,818 issued to Prusinski discloses building blocks made from contaminated scrap materials by a process of mixing and heating, then cooling in molds. While it disclosed the use of a widely varying composition including thermoplastic resins, it did not disclose the use of scraps containing mixtures of thermoplastic and cured thermosetting resins.
U.S. Pat. No. 5,075,057 patented Dec. 24, 1991 by H. K. Hoedl, entitled "Manufacture of Molded Composite Products from Scrap Plastics", provided a procedure whereby scrap plastic materials including thermoplastic and cured thermosetting components may be recycled and molded into products of predetermined shape, without the necessity of separating the different plastics from one another. The patented process included shredding and milling the mixture to reduce it to a fine particle size. The fine particle size mixture was homogenized into a free flowing macrohomogenous powder form. The homogenized mixture was warmed to an elevated temperature at which it maintained its free flowing condition. The warm mixture was dry blended with a reinforcing material or a filler. The blend was then compression molded at elevated temperatures and pressures into a product of pre-determined shape.
U.S. Pat. No. 5,082,605 patented Jan. 21, 1992 by Joe G. Brooks et al, entitled "Method for Making Composite Material", provided a composite material including a discontinuous phase of cellulosic fiber encapsulated in, and bonded to, a continuous phase of a polymeric component containing a major portion of polyethylene. The method included mixing the cellulosic fiber and polymeric component while raising the temperature of the mixture to the encapsulation point. The encapsulated material was maintained within the encapsulation range while the particle size was reduced. Thereafter, the material was extruded while its temperature was controlled within the encapsulation range. The fibers were aligned in the flow direction until the material contacted a heated die. During extrusion, the encapsulated fibers were aligned in the flow direction. As the extrudate passed through the die, the surface temperature was preferably elevated to improve surface properties.
U.S. Pat. No. 5,151,230 patented Sep. 29, 1992 by Dirk H. Damberg, entitled "Process for Production of Products Formed of Polymer Bonded and Granulated Particles", provided an apparatus for continuously manufacturing and forming a cured product of granulate material, polymer glue, and catalyst. The apparatus included a granulator mill which was adapted to shred elastic or inelastic material into small granules and to pass them to a continuous mixer means. A continuous mixer was provided which was adapted continuously to mix a specified amount of inelastic or elastic granulated material, a specified amount of polymer glue, and a specified amount of catalyst. A mold press was provided which received mixed material from the mixer and which molded the mixed material under elevated pressure and temperature into a formed cured product.
U.S. Pat. No. 5,141,688 patented Aug. 25, 1992 by Meirion Gribble, entitled "Method of Making Mineral-Filled Resin Products", provided a method which included thoroughly mixing a powdered mineral material with a minor proportion of a thermosetting resin material. A batch of the resulting formulation, of predetermined weight, was extruded through a rectangular section die to form an elongate extrudate of predetermined length. The extrudate was pressed between a pair of generally planar plates, each of the predetermined length, one of the plates being a cast metal body which had been cast in material bearing an impression of a textured finished building product. The pressed extrudate was then permitted to cure.
U.S. Pat. No. 5,100,603 patented Mar. 3, 1992 by Charles W. Neefe, et al, entitled "Method of Recycling Multimaterial Containers", provided a method whereby empty polymer containers were granulated, mixed with shredded or granulated multimaterial containers and reused to make useful objects without sorting, removing labels or cleaning the containers. The method included cutting the laminated multimaterial containers into granules. The granulated multimaterial was mixed with sugar. That granulated multimaterial granules were mixed with resin granules. The mixture of granules was placed in a mould and the mixture was heated until the resin granules melted, thereby encasing the multimaterial granules. The resins were allowed to cool, and the object was then removed from the mould.
U.S. Pat. No. 4,728,476 patented Mar. 1, 1988 by Douglas J. Boring et al, entitled "Method of Supplying a Moldable Mixture of Materials to an Article Forming Mold of an Injection Molding Machine", provided a method of supplying a mixture of a thermoplastic resin and a low heat conductivity additive to the article forming a mold of an injection molding machine. The mixture was heated in the feed screw of an injection molding machine, to form a flowable mass. Prior to heating, the thermoplastic resin and low heat conductivity additive or filler were mechanically mixed together to form a uniform mixture of resin and filler. After mixing, the mixture was then supplied to the feed screw of an injection molding machine. After such initial heating, the heating of the molten resin/heated filler mixture was continued at a rate to maintain the heated mixture in a standby moldable condition. Prior to the injection of the molten resin/heated filler into an injection machine mold, the molten resin/heated filler was again heated to a higher temperature than the intermediate standby temperature to insure that the plastic article was properly formed.
U.S. Pat. No. 3,880,664 patented Apr. 29, 1975 by Herbert C. Schulze, entitled "Method for Extrusion" provided an improvement in a method for extrusion of materials. Water and cement were mixed before mixing with other ingredients. Fumed silica was also used in the mix.
U.S. Pat. No. 3,991,005 patented Nov. 9, 1976 by Richard A. Wallace, entitled "Structural Material and Method" provided an improved composition predicated upon a discovery that the pyrolysis of incineration residue of industrial or municipal solid waste products was an excellent particulate reinforcement filler material when intimately mixed with an adhesive resinous polymer binder. In carrying out the method of the patented invention, particulate filler was intimately mixed with flowable castable resin binder. Thereafter, the mixture was formed into a desired configuration as by molding or extrusion, and the binder was solidified to form a solid structural composition in which the binder was adhesively bonded to the filler particles.
U.S. Pat. No. 4,280,921 patented Jul. 28, 1981 by John R. May, entitled "Immobilization of Waste Material", provided a method for immobilizing or solidifying waste material which included blending the waste material with powdered metal and subjecting the mixture of waste material and powdered metal to high pressure.
U.S. Pat. No. 5,035,189 patented Jul. 30, 1991 by T. J. Lunsford, entitled "Refuse Recycling System", provided a system for recycling refuse by mixing a predetermined amount of refuse with a predetermined amount of plastic. The mixture was heated until the plastic became liquid. The liquified mixture was formed into a desired shape, e.g., a brick, the mixture was cooled.
U.S. Pat. No. 5,265,545 patented Nov. 30, 1993 to William R. Milner, entitled "Method and Apparatus for Waste Treatment", provided a method of treatment of waste material including the steps of mixing the waste material with a binder and pelletizing the mixture. The pellets were then coated with a non-agglomerating material selected to permit firing of the mixture without pellet agglomeration. The coated pellets were fed to a kiln and fired before being discharged from the kiln. At least some of the heat of firing the pellets was recovered and recycled in the kiln.
U.S. Pat. No. 5,240,656 patented Aug. 31, 1993 by David J. Scheeres, entitled "Treatment of Waste", provided a method and an apparatus for treating contaminated plastics waste. The method included densifying contaminated plastics waste by causing the waste to pass through a heating zone to produce molten contaminated plastics. The molten contaminated plastics was then caused to flow continuously out of the heating zone under the influence of gravity.
U.S. Pat. No. 2,443,289 patented Jun. 15, 1948 by James Bailey, entitled "Apparatus for Shaping Plastics by Extrusion", provided an apparatus for shaping organic plastic materials by extrusion thereof through a die to form elongated or continuous shapes of uniform cross-section. The patented apparatus provided and maintained a separable, and preferably immiscible film of anti-sticking substance or lubricant between the plastic and the die surface.
U.S. Pat. No. 2,769,201 patented Nov. 6, 1956 by Zareh Lorenian, entitled "Screw Extrusion Apparatus for Manufacturing Articles of Thermoplastic and Thermosetting Materials", provided an improved method whereby the material to be worked up was fed into pressing screw or screws tangentially or radially, by means of one or more conveyer screws, which were mounted for rotation in cylinders whose cylindrical surface was formed with interruptions, throughout its length or over part of its length only. The interruptions took the form of recesses of any shape which were arranged longitudinally and whose size and mutual distance was adapted to the actual field of application. These interruptions of the inner cylindrical surface caused the material adhering to the press screw to be torn off or taken off so that the material was at the same time homogenized.
U.S. Pat. No. 4,072,455 patented Feb. 7, 1970 by Erich Beck, entitled "Spiral-Line Press for Thermoplastic Synthetics", provided spiral-line press with a double contra-screw arrangement fixed on a single shaft. The output from the metering zones of the spiral-line were extruded by an outlet fitting which transformed the flows of the extruded matter so that one output was extruded concentrically around the other.
U.S. Pat. No. 2,075,476 patented Mar. 30, 1937 by Albert William Sizer, entitled "Machine for Molding Plastic Substances", provided machines for the molding of plastic substances, mixing machines, continuous crushing or expelling machines of the type in which material was compressed within a chamber by means of a rotary worm element therein. A compression chamber was provided with a worm element having right- and left-hand pitch threading, extending from the centre to the ends respectively. A common inlet was provided for material to be compressed at the centre of the chamber. Die plates were provided at opposite ends of the chamber for the extrusion of compressed material therethrough or alternatively, or additionally, with perforations in the chamber walls for the escape of liquid expressed from the material.
U.S. Pat. No. 4,253,388 patented Mar. 3, 1981 by Luciano Vezzani, entitled "Method and Machine for Compressing and Cutting Random Loaded Scrap Metal", provided a method for compressing and cutting random loaded scrap metal. The method included advancing scrap metal to a cutting zone. A first transversal compression was applied to the scrap metal being advanced. A portion of the scrap metal was guillotined and concurrently a further transversal compression was applied. The machine included a scrap metal conveying trough, a transversally movable pressing plunger adapted for traversing the conveying trough and compacting the conveyed scrap metal, a guillotine block for cutting the compacted scrap metal and a guillotine driven compacting block which was movable perpendicularly to the pressing plunger and cooperated therewith.
U.S. Pat. No. 5,026,512 patented Jun. 25, 1991 by Shao C. Chang, provided a method for manufacturing molded products of thermoplastic material by injection molding or extrusion molding a material containing a thermoplastic material as a primary component and a second polymer or a blend of the thermoplastic material and second polymer as a primary component and an inorganic material. The wall temperatures of the molding cylinder were controlled at different locations of the molding machine. The residence time of the molding material in the cylinder was controlled in response to the cylinder temperature so that the residence time was reduced as the temperature was increased. The temperatures of the discharge end was maintained within the range of the melting temperature of the material.
U.S. Pat. No. 3,411,179 patented Nov. 19, 1968 by Robert B. Gregory et al, entitled "Extruder Screw Mixing Section", provided a plastic extrusion machine including a rotary screw unit having a mixing section at its forward end, which was formed with at least one helical feed channel and at least one helical discharge channel. The feed and discharge channels were so configured as to improve the dispersive mixing ability of the screw in use, i.e., it could simultaneously apply high shear stress upon the higher viscosity thermoplastic constituents and low shear stress upon the lower viscosity thermoplastic constituents. Thereby improved viscosity and temperature homogeneity of the resulting extrudate was attained.
U.S. Pat. No. 3,386,131 patented Jun. 4, 1968 by Marcell Vanzo, entitled "Apparatus for the Continuous Treatment of Rubber and Plastic Material in General", provided an apparatus for the treatment of plastic material. The apparatus included a receiver having a lengthwise extending inlet opening and a discharge opening. A feed screw was rotatably mounted in the receiver and was adapted to feed the material from the inlet opening to the discharge opening. A closing member was quick detachably mounted in the inlet opening to cover a portion thereof in the general lengthwise direction of the receiver. The closing member had an arcuate-shaped portion which formed an uninterrupted continuation of the inner surface of the receiver. The inner surface of the closing member was equally spaced from the addendum envelope of the screw throughout the length of the closing member.
U.S. Pat. No. 5,100,601 patented Mar. 31, 1992 by Anton Heggenstaller et al, entitled "Process for Pressing a Flexurally-Rigid, Beam-shaped Molding", provided a process and devices for producing beam-shaped moldings from fine plant parts mixed with binders in molding presses. The core zone of the molding were formed by an additional amount of fine parts moved there and compacted deliberately. That amount of material acted reactively as a compression zone to the moveable walls surrounding it during the compaction of the molding. Compaction of the molding over its entire cross-section and at the same time particularly great compaction of the peripheral zones of the molding were thus achieved.
U.S. Pat. No. 5,215,695 patented Jun. 1, 1993 by Claudio Bortoluzzi Arenzano et al, entitled "Process for Reclaiming the Residuals of the Manufacture of High Pressure Laminates", provided a process for reclaiming residuals produced from the manufacture of decorative high pressure laminated, and composite materials obtained by the process. Such residuals which included cellulose impregnated with thermosetting resins which were partially condensed, were ground to a predetermined particle size and mixed with a melted mass of thermoplastic resin under controlled pressure and temperature conditions. The mixing time was sufficiently long for completion of the reaction during which physical and chemical interactions occurred between the partially poly-condensed thermosetting resin and the thermoplastic resin. The material so produced was converted into granules for subsequent injection molding.